In order to provide protection against power outages, modern computer systems typically use battery backups. When the AC voltage supplied by a computer's power supply to the computer drops below a certain voltage level, a trigger circuit causes a battery to act as an alternative power source. This allows the computer to save its memory contents during the outage, and if possible, to perform an orderly shutdown. Alternatively, a battery backup system may allow for complete operation of the computer system until AC voltage is restored.
Typically, the battery voltage is supplied by a plurality of battery packs, each containing a plurality of battery cells (usually 6). A battery charger must keep the battery packs charged to assure that the battery will be able to supply the proper level of voltage and energy to the computer when necessary.
Each minute of lost power to a computer system which supports a critical task (for example, processing bank transactions) could result in a loss of hundreds of thousands of dollars. The battery backup helps to minimize these losses and add reliability to the computer system. However, in the event that one battery is damaged, either by a short circuited cell or a by cell with increased impedance, the battery packs may not be able to support the computer system when required. Presently, the deterioration of a battery becomes apparent only when it fails to adequately support the computer system when requested, and data is lost. It would be desirable to have notification of the impending failure of a battery backup system before vital information and computing time is lost.